This invention relates generally to a method of casting an article and more specifically to a method of casting an article having desired crystallographic characteristics. A starter element having the same crystallographic characteristics as the article is used without significant bonding between the cast metal and the starter element.
The concept of casting single crystal articles is disclosed in U.S. Pat. Nos. 3,139,653; 3,759,310; 3,857,436; 4,015,657; 4,111,252; and 4,180,119. The use of a single crystal starter element having a predetermined orientation relative to a mold is disclosed in U.S. Pat. No. 3,139,653.
The use of a chill plate or block having a recess to receive a portion of a single crystal starter element or seed is disclosed in U.S. Pat. No. 3,759,310. The starter element extends only part way across the bottom of the mold cavity. The remainder of the bottom of the mold cavity is defined by a layer of ceramic material which is disposed over the chill plate. In following the teachings of this patent, an electric arc is established between a consumable electrode and the starter element to melt back the starter element. Since the use of an electric arc and melt back of the starter element are analogous to electric arc welding processes, it is believed that significant bonding occurs between the starter element and article being cast with welding of the starter element to the article.